1. Field of the Invention
The present invention relates to an apparatus and method for cleaning a tubular member. More particularly, the present invention relates to an apparatus and method for cleaning a tubular member employing a mixture of a liquid medium and particulate solids.
2. Description of the Prior Art
The interior surface of tubes, pipes, and other tubular members are often cleaned using particulate solids/gas mixtures, liquid mediums such as water, or slurries of particulate solids and liquid mediums. An example of a typical use of these cleaning techniques is the cleaning of the tubes in the tube bundles of heat exchangers commonly used in chemical plants, refineries, and the like.
Generally speaking, the interior of a tubular member such as a heat exchanger tube can be cleaned by forcing a pressurized cleaning medium, e.g.--pressurized gas/particulate solid mixture, water, water/solid slurry--through the tubular member. In this type of cleaning, there is essentially no focusing of the cleaning medium radially outward against the walls of the tubular member, but rather unwanted coatings on the interior wall are removed as the cleaning material moves longitudinally through the tubular member. In an alternative method, a wand or lance can be inserted into the tubular member, the cleaning medium being delivered through the free end of the lance interiorly of the tubular member, the free end generally including a nozzle that serves to accelerate the cleaning medium and direct it radially outwardly against the interior wall of the tubular member.
The use of pressurized gas/particulate solids mixtures--e.g., compressed air and sand--suffers from the disadvantage that as a practical matter the solid particles cannot be accelerated to speeds greater than about 400-500 mph. On the other hand, if the solids are present as a slurry--e.g., in water--they can easily be accelerated to speeds of three to four times that in air. Since the work done by each solid (abrasive) particle is directly related to the kinetic energy of the particle at the time of impact and since kinetic energy is (mass)(velocity).sup.2, it is apparent that impact velocity should be as high as possible to achieve maximum cleaning effectiveness.
In recent years, the use of slurries of water-soluble solids and water as cleaning mediums has become fashionable, primarily because since the solids are water-soluble, clean-up problems are greatly reduced once the cleaning job has been completed. However, these water-soluble solids or abrasives are inherently softer than water-insoluble solids or abrasives. Accordingly, the longer these slurries of water-soluble solids and water remain together and are "handled," the less effective the solids become as cleaning agents because of the fact that, due to attrition and dissolution, they lose the sharp edges and other sharp formations (cutting surfaces) they may possess. Thus, in a typical cleaning system for cleaning tubular members forming heat-exchanger bundles, the particulate solids/water slurry is typically pumped from a holding tank through a lance or other elongate member that can be inserted into the tubular member being cleaned, the slurry then being forced through nozzles that force the slurry in a radially outward pattern against the walls of the tubular member to effect the cleaning. This method necessarily means that the particulate solids in the slurry are in contact with the water for a significant length of time and, moreover, because of being pumped and conveyed through hoses or the like, are subjected to high turbulence, leading to erosion of the cutting surfaces on the particulate solids.